Usually, tires intended for uses on heavy vehicles comprise a carcass reinforcement formed of at least one ply of metal reinforcing elements coated in a rubber material, this reinforcement additionally having the role of withstanding the internal inflation pressure of the tire. This carcass reinforcement is anchored at its ends into tire beads which are intended to come into contact with seats of a mounting rim. The carcass reinforcement may notably be anchored by wrapping it around the circumferential bead reinforcement such as a bead wire. A carcass reinforcement is said to be radial in this document if the reinforcing elements of which it is made make a mean angle greater than 75° with the circumferential direction.
Furthermore, the tire comprises, radially beyond the beads, sidewall zones that experience cyclic variations in curvature during rolling each time they come into contact with the road surface. The carcass reinforcement is also surmounted with a crown reinforcement generally formed of several plies of reinforcing elements crossing one another, this crown reinforcement itself being radially surmounted on the outside by a tread intended to come into contact with the roadway as the tire runs along.
During running, the sidewalls of the tire, and therefore the carcass reinforcement, are subjected to cyclic variations in curvature. These cyclic bending stresses in the reinforcing elements of the carcass reinforcement are amplified when the tire is partially, or even fully, deflated: on the one hand, the amplitude between the maximum radius of curvature and the minimum radius of curvature increases and, on the other hand, the value of the minimum radius of curvature decreases.
This mechanism may, for example, come into play if tires are being used in tandem, one of the tires being partially or completely deflated and the other remaining inflated. When this happens, the carcass reinforcement of the deflated tire is subjected to a low or zero tension, given the lack of inflation pressure, while at the same time being subjected to variations in curvature. These high bending cycles, while the reinforcing elements of the carcass reinforcement are not taut, generate fatigue in the metal reinforcing elements of the carcass reinforcement.
This fatigue of the metal reinforcing elements decreases their rupture strength under tension and may lead to the tire bursting when it is reinflated to its nominal pressure, notably following repair. This problem is known by the name of “zipper failure”. The bursting is accompanied by a failure extending over a shorter or longer circumferential length in one of the sidewalls. With this bursting, an overpressure wave travels through the vicinity of the tire.